From German Patent 36 18 426 and the therein mentioned German Patent 21 19 829 it is known to produce carbon molecular sieves for the separation of gases with small molecular size, particularly O.sub.2 and N.sub.2, in the following manner: finely ground hard coal is oxidized with air in a fluidized bed, after adding binders and water the coal is shaped and carbonized at temperatures up to 900.degree. C., subsequently activated with steam at temperatures of 800.degree.-900.degree. C. and the preliminary product of the low-level activation is treated with carbon splitting hydrocarbons at 750.degree.-850.degree. C.
The carbon molecular sieves produced this way are used for obtaining nitrogen from air in pressure swins processes. The operating costs of alternate pressure processes consist primarily of compression costs for the required air compression. The so-called specific air consumption, i.e. the ratio of the used amounts of air to the produced amount of nitrogen (m.sup.3 air/m.sup.3 nitrogen) should be as low as possible. This specific air consumption is directly related to the nitrogen adsorptivity of the carbon molecular sieve, which results from the difference between the diffusion rates of nitrogen and oxygen in the carbon molecular sieve.